European leaders were shocked this week when Defense Secretary Robert Gates told a NATO audience that the alliance faces a “crisis” because the continent has largely demilitarized. Why the surprise — have they been in a coma?

Europe’s free defense ride — thanks to the rock-solid US security guarantee within the NATO alliance — has been a problem for decades. Taking the US protective umbrella for granted, the continent has raided defense budgets to cover its ever-growing welfare bills.

Just four of NATO’s European members (Bulgaria, France, Greece and Britain) spend the alliance’s recommended benchmark of 2 percent of gross domestic product on defense. Just 2.7 percent of Europe’s 2 million military personnel were deployed overseas in 2007, reflecting badly on NATO’s 1999 pledge to engage in important “out of area” operations.

And it’s no recent trend. Back in 1999, for the NATO air campaign against Serbia, the US provided 100 percent of NATO’s jamming capability, 90 percent of the air-to-ground surveillance and 80 percent of the air-refueling tankers. US fighters and bombers delivered 90 percent of the precision-guided munitions.

The divide’s grown even worse since 9/11, as America has moved into a new political and security space. Now Gates seems to be saying, “Enough’s enough.” America finally appears unwilling to continue shouldering such a disproportionate amount of the regional and global security burden.

Why now? It’s Afghanistan, stupid.

The inequitable sharing of risks and responsibilities playing out there has raised the stakes considerably: America and Britain account for nearly 60,000 of the 86,000 NATO troops. And many more US forces serve outside NATO: By July, we’ll have almost 100,000 in-country; France, Germany, Italy and Spain combined have just 12,000.

But the true disparity is worse. Take one of the crudest indicators of a nation’s commitment to the mission: troop losses. Nowhere do we see a starker picture of who’s actually doing the fighting — and who’s not.

America has lost 1,006 servicemen and -women in Afghanistan. Britain has lost 265 — more than the rest of Europe combined. (It is past time for President Obama to recognize the sacrifice of British servicemen alongside the US military.)

Through 2008, many assumed that continental Europe wasn’t stepping up to the plate because its leaders didn’t like George W. Bush. But nothing’s changed with Obama in the White House: When he asks for more support for Afghanistan, the countries that step up are the same ones that responded to Bush.

When Obama threw his weight behind Gen. Stanley McChrystal’s new strategy, he plainly expected Europe to commit at least 10,000 more troops plus equipment, trainers and money. Yet Europe is sending just over 7,000 more troops — and at least 1,500 of them will come from non-NATO members, including 900 from war-torn Georgia.

And even those numbers overstate Europe’s contribution — because what most of these troops can do is strictly limited by their home governments. As Gates said in 2008, “Some allies are willing to fight and die to protect people’s security, and others are not.”

Although NATO closely guards the comprehensive list of “national caveats,” NATO Supreme Commander Adm. James Stavridis said last June that there were 69. Here’s some of the caveats we know about:

* German troops are restricted to conducting operations in northern Afghanistan before nighttime and never more than two hours away from a well-equipped hospital.

* Turkish troops are restricted to Kabul.

* Troops from most southern European nations are barred from fighting in snow.

* One country prohibits troops from other nations from flying in its aircraft.

Worse, caveats are sometimes unofficial, unwritten and not declared until an operation’s underway, presenting military leaders with the risk that troops they’re counting on can become unavailable after combat’s begun.

Nor is Europe pulling its weight in training and development in Afghanistan. A key part of McChrystal’s counterinsurgency strategy is a rapid expansion of the Afghan Security Forces, requiring nearly 2,500 added NATO or EU trainers. The European Union has dispatched just 281 personnel, only some of them actually trainers. Most are restricted to Kabul, teaching Afghan policemen such pointless tasks as how to issue speeding tickets.

With a few honorable exceptions (such as Britain, Poland, Denmark, Estonia and the Netherlands), NATO’s European members (especially France, Germany, Italy and Spain) have stinted on resources for the UN-mandated mission in Afghanistan. That is, they’ve not only provided too few troops (with too many national caveats) but also too few helicopters.

Save for such warrior nations as Britain, Europe today fundamentally lacks both the military resources and (more important) the political will to fight long wars abroad.

But America doesn’t have the luxury of choosing its wars. And if Europe still believes that the trans-Atlantic security alliance is in its best interests, then it’s going to have to recalibrate its attitude toward war-fighting — and it’s going to have to start with Afghanistan.

Sally McNamara is senior policy analyst in European affairs at The Heritage Foundation.